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std::is_virtual_base_of

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Defined in header <type_traits>
template< class Base, class Derived >
struct is_virtual_base_of;
 (since C++26)

std::is_virtual_base_of is a BinaryTypeTrait.

If Base is a virtual base class of Derived (ignoring cv-qualification), provides the member constant value equal to true. Otherwise value is false.

If both Base and Derived are non-union class types (ignoring cv-qualification), Derived should be a complete type; otherwise the behavior is undefined.

If the program adds specializations for std::is_virtual_base_of or std::is_virtual_base_of_v, the behavior is undefined.

Contents

[edit] Helper variable template

template< class Base, class Derived >
constexpr bool is_virtual_base_of_v = is_virtual_base_of<Base, Derived>::value;
 (since C++26)
[edit]

Inherited from std::integral_constant

Member constants

value
[static]
 true if Derived is derived from virtual base class Base (ignoring cv-qualification), false otherwise
(public static member constant)

Member functions

operator bool
 converts the object to bool, returns value
(public member function)
operator()
(C++14)
 returns value
(public member function)

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>

[edit] Notes

std::is_virtual_base_of_v<A, B> is true even if A is a private, protected, or ambiguous base class of B.

If std::is_virtual_base_of_v<A, B> is true, then std::is_base_of_v<A, B> is also true. However, the converse is not always true because the check for virtual inheritance is more specific. In that case, std::is_virtual_base_of_v<T, T> is false even if T is a non-union class type.

[edit] Example

Run this code
#include <type_traits>
 
class A {};
class B : A {};
class C : B {};
class D : virtual A {};
class E : D {};
 
union F {};
using I = int;
 
static_assert
(
    std::is_virtual_base_of_v<A, A> != true &&
    std::is_virtual_base_of_v<A, B> != true &&
    std::is_virtual_base_of_v<A, D> == true &&
    std::is_virtual_base_of_v<D, E> != true &&
    std::is_virtual_base_of_v<F, F> != true &&
    std::is_virtual_base_of_v<I, I> != true
);
 
int main() {}

[edit] See also

(C++11)
 checks if a type is a base of the other type
(class template) [edit]
(C++11)(C++20)
 checks if a type can be converted to the other type
(class template) [edit]
(C++20)
 specifies that a type is derived from another type
(concept) [edit]
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